Historically, many diverse materials of various origins have been used to treat wounds by absorbing wound fluids and tissue, generally referred to as “exudate,” from a wound site with some type of absorbent material. In recent years, use of polymeric-based wound care products have become increasingly popular to control wound site environmental factors such as water vapor, oxygen permeability, bacterial impermeability, and absorption of exudate. Such wound care products are tailored to meet specific requirements including conformability to a body portion, selective adherence to a wound bed, and adhesiveness to the skin surrounding the wound site.
Recently, occlusive or moisture-retentive dressings have gained increasing acceptance in treating wounds, in particular pressure sores and ulcers. A wide variety of types of structures are known in the art for use in or as wound dressings, and generally comprise components for receiving, absorbing and retaining exudate. Typically, these dressings include polymeric foams, polymeric films, particulate and fibrous polymers, hydrogels and hydrocolloids. Dressings with at least one of these components promote wound healing by providing a moist environment, while removing excess exudate and toxic components, and further serve as a barrier to protect the wound from secondary bacterial infection. While these known dressings can effectively manage a wound, many have been found to possess certain limitations or disadvantages.
Many of the known dressings have an absorbent layer that comprises hydrophilic polymeric foam. Unfortunately, many hydrophilic polymeric foam dressings possess the disadvantage of being limited in the amount of exudate that may be absorbed. The limit in exudate absorption of the foam is often directly related to its overall geometrical size prior to absorbing a fluid. Typically, hydrophilic foams may expand only to 10–20% of their original size. Another disadvantage to hydrophilic foam dressings is that a certain amount of exudate can be “squeezed” out of the foam due to poor liquid retention. The ability of exudates to be squeezed from the foam, and thus dressing itself, poses a risk of infection and may interfere with the healing of the wound.
Yet another disadvantage with known foam dressings is that absorption of exudate by an absorptive layer, such as foam, in contact with the wound causes the central portion of the applied dressing to swell and push up against the wound. Continued swelling can induce separation of the skin adherent layer from the skin outside the wound area, especially at the border of the wound dressing whereat a “curling” effect may occur. This excessive swelling of the dressing may further lead to leakage of the exudate from the periphery of the dressing, thereby providing a tract for the invasion of pathogenic microorganisms and promoting maceration of the wound site.
In many known dressings, a backing layer is provided that comprises a liquid impervious film that is attached to an absorbent layer to prevent exudate from seeping from the dressing. A difficulty arises during fluid uptake in that as the absorbent layer expands, the backing layer must accommodate the expansion of the absorbent layer without causing curling of the dressing.
One solution has been proposed to include a backing layer that is formed of a thin elastic sheet which is yieldable as the absorbent layer swells. It has been found, however, that a liquid impervious plastic film cannot be made to sufficiently stretch in keeping with the expansion of the absorbent layer, and as a result, the film counteracting with the swelling absorbent layer may produce the aforesaid curling at the border of the dressing.
Another solution has been proposed in which a backing layer is attached to the absorbent foam layer and includes a plurality of wrinkles that substantially flatten as the foam layer swells. While the backing layer may accommodate the expansion of the foam layer, the fluid uptake of this dressing is limited by the expandability of the foam layer itself. Accordingly, due to the limited absorptive capacity of the foam layer, the dressing must be frequently replaced.
Ideally, a dressing must have adhesive properties that enable the dressing to attach to the wound site while being non-toxic to skin and eliciting no allergenic response. Moreover, a dressing should possess the ability to prevent bacteria from entering the wound from the ambient environment while providing a suitable moisture transmission rate.
Many known dressings possess the disadvantage of relying solely on a pressure sensitive adhesive layer to secure the dressing to skin. An example of an adhesive is an acrylate glue. While indeed an acrylate glue securely maintains a dressing over a wound, the glue has a tendency to strip the central portion of the dressing from the wound and thus may damage healing tissue.
Wound dressings have been commercially available that include an absorbent foam layer with a skin adherent layer comprising a coating of silicone gel over a surface of the foam layer. According to one solution described in U.S. Pat. No. 6,051,747, the silicone gel coats portions of the walls of the cells of the foam layer to form a plurality of randomly formed apertures. These apertures are created by capillary action when a curable silicone liquid mixture is applied in an uncured state directly to a surface of the foam layer.
It is important to this solution that the silicone mixture be applied to the foam in a liquid state in order for the silicone mixture to be sucked via capillary action into the end portions of the cells near or at the coated surface of the foam layer. Only if the silicone mixture is liquid will the capillary forces of the foam be sufficient to form apertures since overall the capillary forces produced by the foam layer are small. Moreover, the silicone mixture begins to form a gel only after it has started to cure, or more appropriately, cross-link.
This process of coating a foam layer with a liquid silicone mixture and the curing of the same has many inherent drawbacks. One drawback is that some foam cells may not produce sufficient capillary forces to form apertures through the silicone mixture. Thus, some cells may have corresponding apertures in the silicone gel coating while other cells may lack such apertures. Another drawback is that the apertures of the silicone gel coating are randomly formed which may lead to localized areas that inhibit the uptake of the exudate into the foam. This process does not allow the formation of a predetermined pattern of apertures which are uniformly spaced and sized. Thus, there is an overall lack of control of the size, location and density of the apertures.
Another shortcoming to this process and particular dressing is that the surface roughness of the silicone gel coating is largely dependent upon the surface of the foam to be coated. In the event it is desired to obtain a smooth silicone gel layer to be worn against the skin, this approach fails to yield such a smooth silicone layer.
For the foregoing reasons, there is a demand for an improved wound dressing which prevents wound trauma upon repeated dressing changes, improves the durability and lifetime of the dressing, anatomically conforms to a wound, possesses improved fluid uptake, retention and removal properties, and can be securely maintained on a patient's body. It is thus desired to produce a dressing having an adhesive layer that does not possess the drawbacks of known adhesive layers, and instead, gently adheres and detaches from a wound site while providing superior fluid uptake.